Reducing environmentally harmful emissions from internal combustion engines is an ongoing challenge for engine designers. Present and future federal emission standards continue to demand lower emissions for undesirable byproducts of combustion such as soot and nitrogen oxides. Methods for reducing harmful emissions are well known in the art and include thermal management of exhaust gas to reduce formation of nitrogen oxides (NOX) during temperature spikes, and thermal management of exhaust gas to ensure burn off (regeneration) of aftertreatment devices downstream of an exhaust outlet. Known emissions reducing devices and systems include aftertreatment devices such as soot filters to remove particulates from the exhaust gases, and exhaust gas recirculation (EGR) to lower the oxygen fraction of intake air impeding molecular combinations of nitrogen with surplus oxygen that may form NOX.
Although various known methods and devices may answer many of the challenges associated with controlling the release of undesirable emissions, other application specific and circumstantial specific challenges remain unsolved. For example, under steady state operating conditions, NOX emissions for a diesel engine with a manual transmission appear similar to NOX emissions for a diesel engine using an automatic transmission. However, immediately following periods of gear transition, such as during acceleration, the diesel engine with the manual transmission exhibits NOX emission spikes not seen with the diesel engine with the automatic transmission. The diesel engine coupled to the automatic transmission avoids NOX emissions spikes due to the rapid and substantially smooth transitions between gears associated with automatic transmissions, which acts to maintain a load on the engine. The maintained load results in continuing fuel injection, which supports a proper EGR flow and maintains the beneficial oxygen fraction in the intake air.
In contrast to automatic transmissions, engaging the clutch of the manual transmission during gear transitions releases the load from the engine. In response to releasing the load from the engine, the engine may reduce fueling altogether, thereby substantially increasing the oxygen content of the recirculated exhaust and thus raising the oxygen fraction of intake air. When the load is placed back on the engine, air with a relatively high oxygen fraction combusts with reintroduced fuel, which results in high combustion temperatures. Before the engine can achieve a more preferable EGR flow and oxygen fraction (e.g., when the engine reengages the vehicle load by a release of the clutch), the excess oxygen combined with higher exhaust temperatures results in a spike of NOX emissions. Accordingly, the interconnected and delicate balance of preserving fuel economy, meeting acceptable exhaust outlet temperature ranges, maintaining optimal oxygen fraction in the intake air, and generating sufficient air flows in the engine is further complicated and encumbered by the application of the manual transmission.
Though manual transmissions may provide an economical option for consumers, manual transmissions are known to exhibit specific emissions challenges compared to automatic transmissions during periods of gear transition. NOX spikes immediately following transition periods may be so severe with manual transmissions that some manufactures of combustion engines may forego the more economical option of the manual transmissions in favor of more expensive and emissions predictable automatic transmissions.